Near the end of the film, just after Scrooge's transfiguration, he looks at himself in the mirror. A cameraman is clearly visible at this point -- it's pretty hard to miss.
This "slipup" is not only in the old black and white version, but the man can also be seen in the mirror peeking out from behind the curtain in the colorized version of the movie...AND instead of fixing the slipup, he was colorized too!!